A critical aspect of flight operations is the application of brakes during landing to slow the aircraft after touchdown. There are various visual indicators used for landing an aircraft, such as runway markings, distance indicators, and colored lights. These visual indicators are used to facilitate the alignment and position of the aircraft and to indicate the end of the runway. The flight crew may also have use of information obtained during advanced planning, such as runway length, Airplane Flight Manual performance data, and reported runway conditions. Notwithstanding advance planning, operationally, the flight crew must estimate deceleration and the distance remaining to the end of the runway during every landing.
The estimated deceleration is a function of the management of the following critical variables:                a) Runway distance remaining after touchdown to the end of the runway;        b) Runway distance remaining after touchdown to a planned taxiway exit;        c) Runway distance remaining after touchdown to a required stopping point such as an intersecting runway during Land and Hold Short Operations (LAHSO);        d) Runway distance remaining for stopping during an aborted take-off.        
During landing, pilots do not have the ability to verify that the current deceleration is sufficient for the length of runway remaining and that he will not overshoot the end of the runway. Ground based instrumentation for determining if and where an aircraft will stop on the runway is not currently available.
Overshooting the end of the runway is referred to as a runway excursion. Several major risk factors have been associated with runway excursions during landing, which include: go-around not conducted, touchdown long (long landings), ineffective braking technique, contaminated runways, landing gear malfunction, approach fast, fast touchdown, and steep approach angle.
Prevention strategies have been suggested to address these major risk factors. There are two primarily accepted means of mitigating the risk of runway excursions during landing: (1) the development of stabilized approach criteria and stabilized landing criteria, (2) reinforcement of rigorous Standard Operating Procedures. While pursuing means of improving industry best practices is admirable, the critical tasks of estimating and executing a safe stop of an aircraft on the runway under real-time conditions remain with the flight crew.
Electronic vertical and lateral guidance exists during an approach to landing as a primary means to aiding flight crews to achieve a stabilized approach. However, such approach guidance ends upon touchdown, and once on the runway, the flight crew is constantly estimating whether the deceleration level is adequate (with the use of brakes, thrust reversers, and ground lift dumping devices). Similarly, the flight crew must mentally estimate whether the aircraft will have sufficient runway to fully decelerate under the given conditions when take-off is aborted.
To aid the flight crew during landing, certain standardized runway configurations provide visual information such as, stripes, markers at predetermined distances of 500′, 1000′, 1500′, chevrons, and runway light systems for runway maneuvering procedures. Although these visual aids help the flight crew in determining their physical location on the runway, the pilots must continually estimate whether the deceleration rate is adequate to stop the aircraft in the distance remaining on the runway.
During a precision approach, lateral and vertical guidance is intended to yield a stabilized approach with sufficient runway to stop the aircraft. However, during a landing approach, the traditional means of electronic guidance ends when the aircraft passes over the threshold of the landing runway. Upon passing this threshold, the thrust or power levers are retarded to idle and the landing flare is initiated, with all following aspects of the landing being based on the flight crew's personal perception of depth, distance, and deceleration.
Once on the runway, the runway conditions influence whether the aircraft is able to stop before reaching the end of the runway. The flight crew may receive runway condition information from a number of sources, which will affect judgment.
One source of runway conditions is Pilot Braking Action Reports, which can be affected by the reporting crew's experience and the equipment they are operating. The terminology recommended by the International Civil Aviation Organization (ICAO) is “good”, “good to medium”, “medium to poor”, and “poor”; and the Federal Aviation Administration (FAA) is “good”,” “fair,” “poor”, and “nil.” Pilot Braking Action Reports are generally the most recent information available. Therefore, the Pilot Braking Action Report is able to provide information about changing runway conditions.
The airplane's weight, approach speed, amount of wheel braking applied, and the location on the runway where the highest amount of wheel braking is used are factors that influence braking action assessments. Therefore, the flight crew of a small airplane may perceive different braking conditions than the flight crew of a large airplane making these reports subjective.
Sources of runway condition reports may be included in routine notices to airmen (NOTAMs), snow-related NOTAMs (SNOWTAMs), automated terminal information system (ATIS) broadcasts, or via ATC communications with the flight crew. For a short flight, the flight crew may have NOTAMs and/or SNOWTAMs available prior to departure that enable them to perform a preliminary evaluation of the airplane's capability based on conditions reasonably expected at the time of arrival. The flight crew must recognize that conditions may change during the flight and that an update will be required prior to landing. Consequently, all sources of reporting tend to be independent and require additional evaluation in flight with respect to operational decisions. Moreover, even with these sources, information regarding runway conditions may not be available or the conditions may be materially different from those previously reported. Thus, the burden is placed on the flight crew to evaluate the braking operation in real-time.
Runway friction reports is another source for runway conditions. There are several methods available for objectively determining the runway conditions for the runway friction reports. One method uses a vehicle equipped with a decelerometer that measures the deceleration of a test vehicle during a maximum-effort stop, which is converted to a friction rating. Another method measures the force on a braked wheel, typically a towed vehicle, and calculates the friction from the forces on this wheel for typically each third of the runway. However, while ground friction (wheel) reports are typically objective and predictive, the FAA and ICAO warns that ground friction (vehicle) reports are not considered reliable when the depth of contaminant exceeds 1 mm of water; 3 mm of slush or wet snow; or 2.5 cm (1 in) of dry snow. Similarly, such reports may not be measurable under certain conditions and/or the reported frictional measurement can be materially different from that reported, placing the burden on the flight crew to evaluate the braking operation in real-time.
Further, the flight crew may not readily perceive the effect of the real-time braking operation. Accordingly, there is a need for a dynamic real-time indication system and method that overcomes these deficiencies of reports of braking conditions, which are subjective and can quickly become obsolete, e.g. snow, making conditions worse than previously reported.